No abstract available

[en] Since the introduction at SIN of bent-crystal spectrometry for the study of mesic X-rays efforts have been undertaken to improve the resolution without loss of count rate. The angular resolution of bent-crystal spectrometers is primarily dependent on the precision reached in the bending of the crystal. A significant step forward has now been reached with a new type of bending device. Angular resolutions of one arc seconds and better have been reached. (Auth.)

[en] The wavelength of the 25.7 keV γ-ray standard in the decay of ¹⁶¹Tb has been determined as lambda(25.7)=48.334488(64) pm. The present accuracy of 1.3 ppm is higher by a factor of 5 than that of earlier measurements. Simultaneously we have redetermined the wavelength of transitions at 48.9, 67.8 and 74.6 keV with a precision of 1.2, 1.7 and 1.3 ppm respectively. (orig.)

[en] The analysis of pionic atom data of 1s and 2p levels for N=Z spin-zero nuclei, in terms of an improved optical potential is presented. We find a strong (unexplained) s-wave repulsion and evidence for finite-range effects. The need for a relativistic treatment of the pion-nucleus interaction is discussed. (orig.)

[en] With the crystal spectrometer at Muon Channel I at SIN we measured the 3dsub(5/2)-2psub(3/2) X-ray transitions in muonic ²⁵Mg and ²⁷Al. The h.f.s. of the 2psub(3/2) was resoloved and the spectroscopic quadrupole moment of the nuclear ground states determined: Q(²⁵Mg) = +0.201 +- 0.003 b, Q(²⁷Al) = +0.150 +- 0.006 b. We find agreement between the intrinsic quadrupole moment value derived form Q(²⁵Mg) with those calculated from measured B(E2) values. This indicates that for ²⁵Mg the strong-coupling limit of the rotational model with an axially symmetric charge distribution is realized in the lower part of the ground-state rotational band. We combine the quadrupole moments Q with the quadrupole coupling constants measured in electronic atoms of ²⁵Mg and ²⁷Al and derive the electric field gradients as the nucleus (in units of e x a^-3sub(o), where asub(o) is the Bohr radius): [sup(dE)/sub(dz)] = 0.339 +- 0.005 for the ³P₂ state of ²⁵Mg, [sup(dE)/sub(dz)] = 0.54 +- 0.02 for the ²Psub(3/2) state of ²⁷Al. From Hartree-Fock calculations of the ²Psub(3/2) state of Al we derive values for the Sternheimer correction factor R and compare them with calculated values. (orig.)

[en] We have measured the transition wavelengths of the 74.6 keV, 48.9 keV and 25.7 keV γ-lines in the ¹⁶¹Tb decay with a curved-crystal spectrometer. The precision reached are 1.7 ppm, 1.7 ppm and 6.8 ppm, respectively. (orig.)

[en] With the crystal spectrometer at muon channel I at SIN we measured the 3dsub(5/2)-2psub(3/2) transition in muonic ²³Na. The h.f.s. of the 2psub(3/2) level was resolved and the spectroscopic quadrupole moment of the nuclear ground state determined: Q=0.1006+-0.0020 b. Using a collective particle-rotor model description of ²³Na which includes small ΔK=1 admixtures in the wave function, we find agreement between our measured spectroscopic quadrupole moment and the one derive from measured B(E2) values. Combining the quadrupole moment Q with the quadrupole coupling constant measured in the electronic atom of ²³Na, we derive the electric field gradient at the nucleus for two different electronic states: < dE/dz>=0.1185(32)ea₀^-3 for the 3²Psub(3/2) state, < dE/dz>=0.0410(27)ea₀^-3 for the 4²Psub(3/2) state. The field gradient for the 3²Psub(3/2) state is compared with recent many-body calculations of the hyperfine interaction in alkali atoms. (orig.)

[en] The magnetic hyperfine splitting (h.f.s.) in the 1s state of ⁷Li has been measured with a precision of 1% using the bent-crystal spectrometer facility at the SIN muon channel. With an instrumental resolution of 2.5 eV FWHM the h.f.s. was completely resolved in the 2p-1s transition. The result is ΔE(M1)=4684+-49 meV. A comparison of this result with the electromagnetic value yields a new upper limit for the strength of a possible muon-nucleon interaction mediated by an axial-vector boson, which is much lower than those that can be derived from other present data. (orig.)

No abstract available

[en] Motivated by the importance of scalar particles in the current work on gauge theories of fundamental interactions, we have performed an improved muonic-atom experiment to search for long-range muon-hadron interactions. We remeasured the wavelengths of the 3dsub(5/2)-2psub(3/2) X-ray transitions in ²⁴Mg and ²⁸Si with the bent-crystal spectrometer at the SIN muon channel. The relative difference between the X-ray wavelength lambdasub(exp) and the theoretical value as obtained from QED calculations, averaged over the two elements, is theta(-0.2+-3.1).10⁶. Assuming the validity of the QED calculations, we can put limits on an additional muon-nucleon interaction: If such an interaction were mediated, for example, by a scalar or vector (isoscalar) boson with a mass smaller than about 1 MeV, the corresponding coupling constant is gsub(μ)gsub(N)<=0.8.10^-6.e². Alternatively, if additional muon-hadron interactions are negligible, our result corresponds to a 950 ppm test of the vacuum polarisation effect in QED. The result can also be interpreted as a 3 ppm measurement of the negative muon mass. (orig./HSI)